1. Field of the Invention
The present invention relates to a biochip, for example, a biochip in which taper sections are provided, as a means for reducing the width of band, at a sample introductory passage for introducing a sample, in order to improve the detection accuracy. Further, the present invention relates to a biochip having a simple structure so that the sample may be directly supplied into a sample separation passage without requiring the sample introductory passage. The present invention also relates to a method of manufacturing the biochip discussed as above, and relates to an electrophoresis method and an electrophoresis apparatus using such biochip.
2. Description of the Related Art
There has been provided a so-called “electrophoresis method” as a method of separating the electric charge nature matter from protein or nucleic acid. In particular, there is a known method of “capillary electrophoresis method” by using micro electrophoresis chip, in order to separate and fix a very small amount of matter. According to the “capillary electrophoresis method”, a separation object maybe introduced in a separation slot by electro kinetic injection (see, for example, the Patent Document 1).
Patent Document 1: Official Gazette of Japanese Unexamined Patent Publication No. 2000-310613.
According to the Patent Document 1, first, a sample introductory passage and a sample separation passage are provided respectively. Then a small amount of reagent containing a separation object is dropped into a liquid reservoir section of the sample introductory passage. There are electrodes for electrophoresis, respectively provided at this liquid reservoir section, and at another liquid reservoir section located at the other end of the sample introductory passage. When an appropriate voltage is applied to these electrodes for electrophoresis, the sample dropped into the sample introductory passage moves to an intersection part at which the sample introductory passage perpendicularly intersects with the sample separation passage.
When the sample reaches the intersection part, an appropriate voltage is applied to other two electrodes for electrophoresis, respectively provided at other two liquid reservoir sections located at the both ends of the sample separation passage. Consequently, the sample existing only at the intersection part will be separated, and move inside the sample separation passage in the form of band, thus it is possible to carry out the optical detection at a predetermined measuring point. In this connection, the “optical detection” would mean, for example, that the optical absorbance is measured by using the UV (ultra violet) absorption property of nucleic acid molecule, or the size of nucleic acid molecule is detected by marking fluorochrome on the nucleic acid molecule so that the fluorescence may be measured.
However, the above prior art has the following disadvantages.
As discussed above, according to the prior art, the introduced sample moves to the intersection part by electrophoresis, and only the sample that reached the intersection part will then be separated and move inside the sample separation passage, and eventually will reach detecting sections respectively provided at each end of the sample separation passage. At that time, during movement of the sample, the width of the band of sample existing at the intersection part will be expanded due to molecular diffusion, thereby the detected image of electrophoresis will become unclear, which would result in a poor detection accuracy. In particular, the larger the number of base becomes (such as DNA), the lower the detection accuracy would become, and due to the difference of base number, the complete separation cannot be done.
Further, according to the prior art, the sample is first introduced from injection holes to the sample introductory passage, and then the sample is introduced to the sample separation passage being provided independently. Thus, even a sufficient volume of sample is injected from the liquid reservoir sections, the amount of sample, actually entering the sample separation passage to be used for separation, is very little, and the large amount of the sample, i.e. the remaining sample, will become useless.
In addition, as discussed above, since the two-phase electrophoresis, i.e. the introductory electrophoresis and the separation electrophoresis is required, the apparatus related to the electric power supply would become complicated.